1. Field of the Invention
The present invention relates to a grooved nut secured to a variety of members to fasten a bolt and the like and relates to a fastening technique.
2. Description of the Related Art
Known as a nut to be attached to metal plates forming various kinds of devices and apparatuses is, for example, such a calking nut device as disclosed in Japanese Patent Laying-Open No. 2000-15527. The device is designed to thrust a nut by force from above into a lower hole of a metal plate disposed on a die to increase a diameter of its distal end portion, thereby attaching the nut to the metal plate.
Another well-known grooved nut is that called self-clinching nut for use in attaching a nut to a relatively flexible material such as an aluminum plate.
The grooved nut is formed to have a cylindrical shaft portion having a screw hole at its center, a head portion whose outer periphery is polygonal and which is provided at one end portion of the shaft portion, and a peripheral groove provided at a boundary part between the head portion and the shaft portion, so that with the shaft portion inserted into an attachment hole provided in advance at such a member as an aluminum plate to which attachment is made, thrusting the head portion into the member to which attachment is made by pressing or the like results in plastic deformation of the member to which attachment is made caused by the thrusting of the head portion to make a mass of the member in question to flow into the peripheral groove, thereby securing the whole nut in question to the member to which attachment is made with the nut whirl-stopped by the thrusting of the polygonal head portion by force.
Using the present grooved nut more facilitates its attachment work than that by welding or the like to improve productivity of the device or apparatus in question.
Conventional grooved nuts, however, have the following shortcomings because they are formed by cutting out a bar member whose sectional configuration is polygonal to correspond to the configuration of a head portion of the nut into a predetermined size and then forming a shaft portion and a peripheral groove by a cutting process.
More specifically, when the peripheral groove is formed by the cutting process, a fiber flow of the material is cut off at the peripheral groove portion. On the other hand, the peripheral groove portion is a part smaller in diameter than other portions and smaller in thickness of a mass when it is hollow, and also a part on which stress is liable to concentrate, so that the peripheral groove portion is liable to lack a strength and break.
In addition, since the width of the peripheral groove is narrow, a tool for forming the groove by the cutting process should have a narrow tip, whereby the tool is liable to break, be damaged or abrade to cause reduction in working efficiency or increase in costs.
Consequently, it is an object of the present invention to provide a grooved nut having a peripheral groove portion whose strength is high enough and which causes none of breakage, damage or the like of a tool at the manufacturing.
According to one aspect, the present invention relates to a grooved nut which has a cylindrical shaft portion having a screw hole at its center, a head portion whose outer periphery is polygonal and which is provided at one end portion of the shaft portion, and a peripheral groove provided at a boundary part between the head portion and the shaft portion, in which the peripheral groove is formed by a plasticizing process.
According to the grooved nut, since fiber flow of a material will not be cut off in the vicinity of the peripheral groove, a desired strength is ensured even when the thickness or the diameter of the groove portion is smaller than that of other portions.
According to another aspect, the present invention relates to a method of manufacturing a grooved nut which has a cylindrical shaft portion having a screw hole at its center, a head portion whose outer periphery is polygonal and which is provided at one end portion of the shaft portion, and a peripheral groove provided at a boundary part between the head portion and the shaft portion, in which the head portion at the tip and the peripheral groove continuous thereto are formed by decreasing the diameter of one end portion of the cylindrical material having a lower hole of the screw hole provided at its center by a pressing process to make its major diameter smaller than those of the other portions, as well as increasing the distal end side of the smaller diameter portion by a pressing process while constraining the proximal end thereof by using a split mold.
According to the present invention, a grooved nut in which no fiber flow is cut off at the peripheral portion according to one aspect of the present invention is manufactured, while the need of a tool having a narrow tip for forming the peripheral groove is eliminated to prevent break, damage or early abrasion of tools.
According to a further aspect, the present invention is characterized in that at the formation of the head portion by the pressing process in the above-described invention according to another aspect, the outer peripheral of the head portion is formed to be polygonal. Moreover, according to a still further aspect, the present invention is characterized in that also in the above-described invention according to another aspect, after the head portion is formed by the pressing process, the outer peripheral portion of the head portion is formed to be polygonal by trimming.
Of these inventions, the invention according to the further aspect eliminates the need of other steps of forming the head portion into a polygonal configuration when the polygonal configuration of the head portion is relatively simple configuration such as pentagon.
In addition, the invention according to the still further aspect enables formation of the head portion to high precision even when its polygonal configuration is relatively complicated such as serration or gear form.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.